Chain link and method for making same

ABSTRACT

This invention relates to chain links, and, more particularly, to a chain link adapted to form a part of an endless drive chain for power transmissions and the like. The invention also relates to a method for making the chain link of the invention.

I United States Patent 1 51 3,636,788

Jeffrey 1 Jan. 25, 1972 CHAIN LINK AND METHOD FOR rences Cited MAKINGSAME UNITED STATES PATENTS [721 2,667,791 2/1954 Bremer ..74 245 5 [73]Assignee: Borg-Warner Corporation, Chicago, Ill.

. Primary Examiner-Leonard H. Gerin Flledl J 1970 Attorney-Donald W.Banner, Lyle S. Motley, C. G. Stallings [2]] APPL No; 8,143 and WilliamS. McCurry Related U.S. Application Data [57] ABSTRACT [62] Division ofSer. No. 572,590, Aug. 15, 1966, Pat. No. This invention relates tochain links, and, more particularly, to 3,535,871, a chain link adaptedto form a part of an endless drive chain for power transmissions and thelike, The invention also re- [52] U.S. Cl. ..74/250 S, 74/245 S lates toa method for making the chain link of the invention. [51] lnt.Cl. .L..Fl6g 13/02 58 Field of Search ..74/250 s, 245 s, 251 s, 253 s, 2Claims, 4 Drawmg Flgures PATENTEU JAN 2 5 1572 MOE INVENTOR JO EPH O.JEFF CHAIN LINK AND METHOD FOR MAKING SAME The present application is adivisional application of Ser. No. 572,590, filed Aug. 15, 1966 andentitled CI-IAIN LINK AND METHOD FOR MAKING SAME.

The invention is concerned with improved chain links of the invertedtooth type in which the link teeth are delineated by a recess bounded bythe inside flanks of the teeth and the crotch of the link. Applicant hasfound that service failures of this type of chain generally occur byfatigue, characterized by the initiation of a crack on the surface of alink in the region of the crotch. The crack then propagates into one ofthe link apertures or through the waist of the link until the remainingcross section diminishes to the point where it can no longer transmitthe chain load and final fracture occurs without warning. It is,accordingly, a principal object of the invention to provide an improvedchain link with enhanced resistance to fatigue failures initiating inthe region of the crotch.

Another object of the invention is to provide a chain link which ischaracterized by favorable internal residual stresses on the surface ofthe crotch portion and extending outward therefrom along the insideflanks of the teeth of the link.

A further object of the invention is to provide a chain link of aparticular design in which the improved fatigue characteristics areachieved without altering the form or configuration of the finishedlink, the material from which it is made, or the manufacturing andproceming operations normally involved heretofore in the production ofthe chain link.

An additional object of the invention is to provide improved fatigueresistance and power transmission capacity without increasing the massof the chain link.

A further object of the invention is to provide a more fatigue resistantchain link which can be made interchangeable with the links of existinginverted tooth-type chains.

A further object of the invention is to provide a chain link in whichfatigue resistance is further enhanced by providing a surface on theinner flanks of the teeth which is smooth, hard and burnished.

Another object of the invention is to provide, for inside engagementchains, a chain link having a more precise contour on the inside flanksof its teeth thereby improving the engagement characteristics betweenthe chain link and sprocket teeth.

A further object of the invention, also applicable to inside engagementchains, is to provide smooth, hard and burnished surfaces on the insideflanks of the teeth of the link, thereby improving the wear resistanceof the chain.

A further object of the invention is to devise a method for making animproved chain link.

Other and more particular objects and advantages of the presentinvention will be apparent from the following detailed descriptions andthe attached drawing, wherein:

FIG. 1 is a fragmentary elevational view illustrating a section of powertransmission chain made in accordance with the present invention andillustrated in operative relation to a sprocket;

FIG. 2 is an elevational view illustrating the blank from which one ofthe links of FIG. I is formed;

FIG. 3 shows the blank as it appears in position on the fonning die, thefunction of which is to spread the teeth of the blank far enough apart,when a force is applied on top of the blank, to produce the internalbending stress pattern illustrated across the waist of the link; and,

FIG. 4 is an elevational view illustrating one of the links of FIG. 1 inits finished form and containing the residual stress pattern illustrateddiagrammatically across the waist portion of the link after springingback to the desired final dimensions.

Referring to the drawing, and more particularly to FIG. 1, there isillustrated therein an endless power transmission chain indicatedgenerally by reference numeral and including a plurality of interleavedseries of links 12 each having a pair of substantially symmetrical teeth14 whose inner flanks 15 terminate in a crotch 17 of the link, saidinner flanks l5 and the crotch 17 thereby delineating a recess space 16between the teeth 14. Each link 12 has an edge 19 which is illustratedin FIGS. 1 and 4 as being slightly crowned. FIG. 3 illustrates a linkblank of the type shown in FIG. 2 and in the configuration ittemporarily assumes during the forming operation accord ing to thepresent method. In that condition the top portion is illustrated asbeing somewhat flattened, and the recess space between teeth 28 isdilated by the forming die 34 forcing the teeth 28 outward therebymaking the recess space temporarily greater than the recess space 16 oflink 12. It will be appreciated that the top portion 32 of link blank 26may be as signed other configurations and the condition it temporarilyassumes during the forming process is irrelevant. Each series of linksis hingedly connected to an adjacent series of similar links in order topermit articulation of the chain around sprocket 20. The chain, asillustrated, is adapted for engagement by teeth 18 of a sprocket 20against the inner flanks l5 of the chain link teeth 14. By suitablyenlarging the recess space 16 between the teeth 14 of the links, it isapparent that engagement could be effected between sprocket teeth 18 andthe outer flanks of chain link teeth 14. Each of the links 12 isprovided with a pair of apertures 22 for reception of a suitable pintleassembly 24, an example of which is illustrated in FIG. 1.

According to the present invention, each link 12 is initially formed asa blank 26 illustrated in FIG. 2. The blank 26 has essentially the samebasic configuration as that of the finished link 12 except that thelinear distance between the bottom tips of the teeth 28 in blank 26 isshorter than the distance between the same tooth tip points in thefinished link 12. Thus, the recess space 30 delineated by the crotch l7and inner flanks of the teeth 28 in blank 26 is smaller than the recessspace 16 of the link 12. The blank 26 has a pair of apertures 22 whichare identical with the apertures 22 in the finished link 12, asillustrated in FIGS. 1 and 4. Under certain manufacturing conditions,the operation of forming the finished link 12 from the blank 26 may befacilitated by providing top surface 32 of blank 26 with a convexcurvature, as illustrated in FIG. 2, although this configuration is notessential to the fulfillment of the inventors basic objectives.

According to the method of the present invention, the link blank 26 ismodified by a cold-forming operation which temporarily enlarges therecess space 30 by a predetermined amount greater than the desiredrecess space 16 of the finished link 12. Removal of the cold-formingforces permits the deformed blank to spring back to the desired finalshape of the link 12, at the same time inducing favorable residualcompressive stresses in the critical region of the crotch 17, therebyenhancing the fatigue endurance strength of the link.

The temporary enlargement of the recess space described above is bestillustrated in FIG. 3, which shows the residualstress-forming die 34 inposition between teeth 28, while a force is applied on the top of theblank, the downward movement of which causes the teeth 28 to be forcedoutward. The configuration of the die 34 and the extent of downwardmovement of the link blank thereon are chosen to permanently deform theblank by the amount necessary to induce the desired residual compressivestresses in the crotch region of the link upon removal of the deformingforce and concomitantly to obtain the required final shape of the link12. During the application of the deforming force, the upper portion ofthe link blank between the crotch l7 and top portion 32 is subjected tobending stresses, the relative magnitude and distribution of which areshowndiagrammatically by the stress pattern 36 in FIG. 3. The portiontoward the crotch is subjected to tensile stresses in excess of theyield strength of the material, while compressive stresses prevail inthe portion nearer the top portion 32.

FIG. 4 illustrates the finished link 12, which, upon removal of thedeforming force, has the required configuration as well as the desiredresidual stresses, the relative magnitude and distribution of which areshown diagrammatically by the stress pattern 40-42. Around the crotch17, where fatigue cracks would originate, favorable residual compressivestresses 42 now prevail, balanced by tensile stresses 40 near the top 19of the link 12.

Because the inner flanks of the teeth 14 of link 12 have been formed bysliding under pressure on the faces of the residual-stress-forming die34 in FIG. 3, these inner flanks will have a more precise contour thancan be achieved by conventional forming methods, e.g., blanking. Inaddition, the inner flanks 15 of the teeth 14 of link 12 will havesmooth, hard, burnished surfaces, free of burrs, also attained bysliding under pressure on the faces of forming die 34. In chain drivesdesigned to have the sprocket teeth engage the inner flanks of the chainlink teeth, all of the above features would be especially desirable asthey contribute to a smooth running chain with reduced wear and noise.

Due to the wedging action of the residual-stress-forming die 34 betweenthe teeth 28, only relatively small forces are required to produce therequired displacement of the teeth in the forming operation shown byFIG. 3. Such forces may be effected by hand tools, such as a hammer,vice, arbor press or the like, or by a power driven reciprocating die.Another feasible method would be to run an assembled chain over asprocket having suitably enlarged teeth while pressing a roller down onthe top of the chain directly over the sprocket, thereby forcing thelinks down far enough on the enlarged sprocket teeth to effect thedesired link tooth displacement.

I The method of the present invention involves the steps of:

a. forming a link blank having at one side thereof a pair of teeth withinner flanks which terminate in a crotch, the inner flanks and crotchdelineating a recess space between the teeth, the linear distancebetween the tips of said teeth being less than that desired in thefinished link;

b. applying a cold-forming operation on said link blank whereby theteeth are forced outward causing the linear distance between the tips ofthe teeth to exceed that desired in the finished link; and,

c. terminating the cold-forming operation at a point which allows thetemporarily deformed link blank to spring back to the desired finaldimensions and configuration of the finished link and having inducedtherein favorable residual compressive stresses in the critical regionof the crotch thereby enhancing the fatigue strength of the link. itwill be appreciated by those skilled in the art that the steps describedabove must be performed subsequent to any heat treatment of the link inorder to retain the favorable residual stresses induced therein.

As a means of producing a more accurately sized and precisely shapedcontour delineating the recess space of the link blank prior to heattreatment, the method of the present invention may be utilized in thefollowing manner:

a. forming a link blank preform having at one side thereof a pair ofteeth with inner flanks which terminate in a crotch delineating a recessspace between the teeth, the linear distance between the tips of saidteeth being less than that desired in the finished link blank;

b. applying a cold-forming operation on said link blank preform wherebythe teeth are forced outward causing the linear distance between thetips of the teeth to exceed that desired in the finished link blank;and,

c. terminating the cold-forming operation at a point which allows thetemporarily deformed link blank preform to spring back to the desiredfinal dimensions and configuration of the link blank. Heat treatment ofthis link blank would alleviate or remove any residual stresses therein,after which the steps describedin the preceding paragraph would beapplied to attain the finished residually stressed link having enhancedresistance to fatigue failures in the region of its crotch, togetherwith precision inner flank contours of superior smoothness and hardness.

The amount of prestress may be readily determined by measuring the forceapplied to the link.

The invention contemplates the extension of the forming die fully intothe crotch when the force is applied on the link to spread the teeth. Bythis expedient more precise shaping of the link may be effected andadditional cold working may be provided by upsettin the crotch. y

The chain link of e present invention exhibits superior resistance tofailure in the critical area around the crotch, where fatigue cracks aremost likely to originate. Applicant has found that there is nodeleterious distortion of the remainder of the link due to theresidual-stress-forming operation. The apertures 22, for example, areidentical before and after the forming operation. The method of thepresent invention is simple, inexpensive, and capable of being performedby inexperienced help.

Applicant does not intend to be limited by the above descriptions, butintends to be limited only by the scope of the appended claims.

I claim:

1. A drive link for an endless chain, said drive link having, at oneside thereof, a pair of spaced teeth defined by a recess terminating ina crotch, a waist zone extending between said crotch and the other sideof said link, said waist zone being prestressed to increase fatigueresistance.

2. A link in accordance with claim 1, in which favorable residualcompressive stresses have been induced in the region of the crotch.

1. A drive link for an endless chain, said drive link having, at one side thereof, a pair of spaced teeth defined by a recess terminating in a crotch, a waist zone extending between said crotch and the other side of said link, said waist zone being prestressed to increase fatigue resistance.
 2. A link in accordance with claim 1, in which favorable residual compressive stresses have been induced in the region of the crotch. 